Many modern turbine engine airfoils, such as blades and vanes, are constructed of a composite laminate or molded fiber. Airfoil metal leading edge (herein “MLE”) protective strips can be used to protect composite airfoils from impact and erosion damage that can often occur in the engine environment. In conventional practices, a v-shaped protective metallic strip is often wrapped around the leading edge and sides of the airfoil to provide such protection.
While MLE protective strips can be made from a variety of materials, titanium and titanium alloys are often utilized due to their favorable weight and mechanical properties. However, hot forming methods must be used to fabricate these titanium components. Hot forming typically involves multiple steps with intermediate chemical milling or machining. This can lead to high tooling costs, high yield losses, and environmentally unfriendly processing. These drawbacks are especially true when fabricating thin, complex geometries, such as MLE protective strips.
Additive manufacturing involves the buildup of a metal part or preform to make a net, or near net shape (NNS) component. This approach can make complex components from expensive materials for a reduced cost and with improved manufacturing efficiency. Generally, a freestanding component is built from a computer aided design (CAD) model. However, when the component has a thin and/or complex shape, it can be beneficial to build up the component on a tool for support.
When a high temperature, melt-based process, such as plasma transferred arc or laser cladding, is used as the additive method to make a NNS component, the tool must perform several functions: it must give shape to the part, it must control heat input to provide a uniform microstructure over the entire length of the component with the desired grain size, and it must conduct heat away from the deposit rapidly enough to prevent fusion of the deposited component to the tool. Additionally, the tool must not cause any contamination of the metallic deposit, as contamination can have a disastrous affect on the physical and mechanical properties of the component. This is especially true when working with titanium and titanium alloys.
More specifically, when titanium or titanium alloy is deposited, the risk of contamination of the deposit by the tooling is high due to the high melting point and reactive nature of titanium. Current practice utilizes a monolithic tool made from the same alloy that is being deposited (e.g. titanium or titanium alloy). While this approach helps mitigate the issue of contamination, it results in a very narrow process window for making a sound deposit without fusion of the deposit to the tool. This is because titanium is a relatively poor heat conductor when compared to other heat sink materials (e.g. refractory metals, mild steel, copper).
Accordingly, there remains a need for manufacturing methods that address and overcome the previously discussed issues associated with current MLE protective strip manufacturing.